In general, the timekeeping hands in watchmaking parts are fixed onto their rotational arbor by driving, i.e. a hollow cylinder, in this case the cannon, is forced onto an arbor with a diameter that is slightly greater than the internal diameter of the cylinder. The elastic and plastic properties of the material that is employed, generally a metal, are used for this driving operation. Thus, it is possible for a hollow cylinder to be driven onto a conventional rotational arbor, such as those that are used in mechanical horology, with a difference in diameter of several microns.
Furthermore, fixing a hand must provide a force that is sufficient to be able to retain the hand in place in the event of impacts. The force needed for a conventional timekeeping hand is approximately 10 N, for example.
In order to overcome these problems, it has already been proposed for the hands to be produced with a cannon having one or more slots that are parallel to the rotational arbor and are open at the end opposite the hand so that the cannon deforms elastically. Such an example of fixing is particularly disclosed in document EP 1659460.
The timekeeping hand described above has several disadvantages. Firstly, it is to be noted that the slots on the cannon weaken this cannon, which involves producing extremely thin slots so as not to excessively weaken the cannon. It is also to be noted that complex machining operations are involved in obtaining the finest possible slots, whilst complying with the width and the length required to obtain the desired driving force, which involves an increase in production costs and time.